// User-level IPC library routines

#include <inc/lib.h>
// Receive a value via IPC and return it.
// If 'pg' is nonnull, then any page sent by the sender will be mapped at
//	that address.
// If 'fromenv' is nonnull, then store the IPC sender's envid in *fromenv.
// If 'perm' is nonnull, then store the IPC sender's page permission in *perm
//	(this is nonzero iff a page was successfully transferred to 'pg').
// If the system call fails, then store 0 in *fromenv and *perm (if
//	they're nonnull) and return the error.
//
// Hint:
//   Use 'env' to discover the value and who sent it.
//   If 'pg' is null, pass sys_ipc_recv a value that it will understand
//   as meaning "no page".  (Zero is not the right value.)
int32_t
ipc_recv(envid_t *from_env_store, void *pg, int *perm_store)
{
	// LAB 4: Your code here.
	if(pg == 0)
	{
		//address above UTOP will be regarded as no page
		if(sys_ipc_recv((void*)UTOP) != 0)
			panic("ipc recv error");
	}
	else 
	{
		if(sys_ipc_recv(pg) != 0)
			panic("ipc recv error");
	}
	if(from_env_store != 0)
		*from_env_store = env->env_ipc_from;
	if(perm_store != 0)
		*perm_store = env->env_ipc_perm;
	return env->env_ipc_value;
	//panic("ipc_recv not implemented");
	//return 0;
}

// Send 'val' (and 'pg' with 'perm', assuming 'pg' is nonnull) to 'toenv'.
// This function keeps trying until it succeeds.
// It should panic() on any error other than -E_IPC_NOT_RECV.
//
// Hint:
//   Use sys_yield() to be CPU-friendly.
//   If 'pg' is null, pass sys_ipc_recv a value that it will understand
//   as meaning "no page".  (Zero is not the right value.)
void
ipc_send(envid_t to_env, uint32_t val, void *pg, int perm)
{
	// LAB 4: Your code here.
	int ret;
	void * srcva;
	if(pg == 0)
		srcva = (void*)UTOP;
	else
		srcva = pg;
	while(1)
	{
		ret = sys_ipc_try_send(to_env,val,srcva,perm);
		if(ret == 0 || ret == 1)		
		{
			//cprintf("return 0\n");
			sys_yield();
			break;
		}
		else if(ret == -E_IPC_NOT_RECV)
		{
			//cprintf("ipc not recv\n");
			sys_yield();
			continue;
		}
		else
			panic("error occur in ipc send:%e",ret);
	}
	//cprintf("return from ipc send\n");
	//panic("ipc_send not implemented");
}

